The present invention relates to an electro-analytical measuring process and apparatus for the selective, rapid and high-precision determination of the concentration and the ion-activity of stationary or flowing solutions or of the partial pressure of gases.
It is well known that an electro-chemical measuring chain is composed of several parts--sensing element or elements and reference electrode or electrodes. Consequently, the measuring signal obtained at the relevant outputs of the measuring chain appears as the resultant of several current or voltage signals, generally as an algebraical amount. Consequently, in the case of some undesirable change, a disturbance occurs at any of the elements of the measuring chain arranged in a measuring cell of traditional construction, resulting e.g. from thermic or "aging" reasons, this cannot be distinguished from the range of the signal incurring as a result of the change of the parameter to be measured, e.g. increase or decrease of the sample-concentration.
Obviously, traditional measuring techniques calibration, standard addition, setting of the constant ion-intensity, programming of slope, etc., see e.g. Havas: Ion and molecule selective electrodes in biological systems and latest results of chemistry, published by: Akademiai Kiado in 1980, pages 80 to 87 do not strive, since they cannot strive to determine the extent of the fault-signal resulting from the disturbances already mentioned. All things considered, the methods known till now may be attributed to the comparison of the relevant electrochemical parameters of the sample and of one or more liquids, standard solution or gas, of a known composition. It means that before the measurement is carried out, the electronic behavior of the measuring equipment and the electrochemical behavior of the measuring equipment and the electrochemical behavior of the measuring cell are to be harmonized--this is called; matching.
As a consequence of the uncontrollable irregularity of the disturbances occurring, the accuracy of the measurements depends obviously on the frequency of the above matching or matchings. In precision measurements it is required to carry out some matching prior to each and every measurement--at least for the sake of control. If the time necessary for the indispensable flushing of the measuring cell is also considered, the total period of the analysis will be--in the case where two standard liquids are applied--approximately five times more than the actual period of the measurements. Though by "one-spot" matching wide spread in electro-analytics this period may be reduced to one half, there is a fault resulting from the interim change of the response-function slope of the measuring cell that cannot be eliminated.
The incidental fluctuation of the electro-chemical parameters of the measuring cell is not the only reason for frequency matching. This is required also for the reason that the long-time stability of the measuring equipment cannot be unlimited because of principle-electro-analytical reasons.
It is obvious from the above that the total period of the precision analysis is considerably long--because of the matching steps between factual measurements. On the other hand, it is impossible to carry out continuous, and at the same time high-precision measurements, as the construction of traditional measuring cells does not factilitate the determination of the fault signals during measurement, not speaking of matching to be performed simultaneously with the measurement.